Overview

This experiment looks simple — a bowl of water and one drop of coloring — but the results are mesmerizing. Instead of instantly turning the entire bowl one color, the drop forms delicate ribbons that drift and swirl through the water. Students can observe density, surface tension, diffusion, and currents all at once.

Materials

You will need:

• A bowl (a cereal bowl or shallow dish works well)
• Water
• A spoon
• Liquid food coloring

Procedure

1. Prepare the Bowl

Fill the bowl with water.
Give the water one quick stir with a spoon.

Let it rest for about 30 seconds.
It will look still — but tiny currents will continue moving inside.

2. Add the Drop

Place one drop of food coloring very gently near the center of the bowl.

Watch carefully for the next few minutes.

What You’ll See

Instead of instantly mixing, the coloring:

• Releases thin strands
• Forms slowly growing streamers
• Drifts outward in curving patterns
• Moves even though you’re not stirring

If you used a big drop, some coloring may even pool on the bottom before spreading.

This is a wonderful moment to pause and observe.

The Science Behind the Patterns

This demonstration beautifully combines three concepts: density, surface tension, and turbulent motion.

1. Density Differences

Food coloring mixed with water is slightly denser (heavier) than plain water.

• Denser liquids sink.
• Lighter liquids rise or drift higher.

If the drop is large enough, you may see a “blob” sink before spreading along the bottom.

2. Diffusion (Brownian Motion)

Inside the bowl, water molecules are always moving — even when the water looks still.

They:

• Vibrate
• Slide around
• Bump into other molecules

When the fast-moving water molecules collide with slower, heavier dye molecules, they gradually push them outward. This slow spreading is called diffusion, and it happens because of Brownian Motion.

It’s like tossing soft balls at a box:

• An empty box moves easily
• A heavy box moves less
• But it still moves a little each time

The dye “box” moves slowly but steadily.

3. Surface Tension Barriers

Water molecules cling tightly to each other at the surface — forming a flexible “skin.”

Food coloring can change this surface tension.

Because:

• The water at the surface has one tension
• The water mixed with dye has a slightly different tension

They don’t blend right away.
A temporary, thin “boundary layer” forms between the two liquids.

Over time, that barrier weakens as molecules mix.

4. Hidden Currents from Your Stir

Before adding the dye, you stirred the water.
Even though it looked still after 30 seconds:

• Tiny spirals
• Slow currents
• Pockets of rising and sinking water

…continued moving.

These gentle currents help pull the coloring outward in fine lines.

That’s why the dye seems to “grow” and “crawl” through the bowl, even without stirring.

What Students Can Explore

For Younger Students:

• Draw the patterns they see
• Describe the shapes
• Compare color movement over time

For Older Students:

• Try different temperatures of water
• Add more than one drop in different locations
• Compare “tap water vs. salt water”
• Use a clear cup to view vertical movement (sinking / rising dye)

For Middle Grades:

• Discuss diffusion vs. convection
• Write a short explanation of how molecular motion creates the effect
• Time how long it takes for the bowl to become fully colored

Teacher Notes

This simple setup illustrates:

• Density
• Surface tension
• Diffusion
• Residual currents
• Molecule motion

…and it does so in a way that feels almost artistic. This makes it an excellent demo for science units, STEAM lessons, or even mindfulness observation exercises.